Quantum dot light-emitting device and preparation method thereof

ABSTRACT

The present disclosure relates to the technical field of display, and discloses a quantum dot light-emitting device and a preparation method thereof. The quantum dot light-emitting device includes a first electrode layer, a quantum dot light-emitting layer, an electron transport layer, a second electrode layer and a third electrode layer which are sequentially arranged in a stacked manner, wherein the side, facing away from the first electrode layer, of the third electrode layer is configured as a light exiting side; the second electrode layer and the third electrode layer are transparent electrode layers; and the work function of the second electrode layer is greater than the LUMO energy level of the electron transport layer and smaller than the work function of the third electrode layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a National Stage of International ApplicationNo. PCT/CN2019/125757, filed on Dec. 16, 2019, claims priority toChinese Patent Application entitled ‘QUANTUM DOT LIGHT-EMITTING DEVICEPREPARATION METHOD AND QUANTUM DOT LIGHT-EMITTING DEVICE’ filed on Jan.11, 2019 by the Chinese Patent Office with Application No.201910027598.6, the entire contents of which are incorporated herein byreference.

FIELD

The present disclosure relates to the technical field of display, inparticular to a quantum dot light-emitting device and a preparationmethod thereof.

BACKGROUND

As a novel light-emitting material, a quantum dot QD has the advantagesof high light color purity, high light-emitting quantum efficiency,adjustable light-emitting color, long service life and the like, andbecomes a research hotspot of the current novel LED light-emittingmaterial. Therefore, a quantum dot light-emitting diode QLED using thequantum dot material as a light-emitting layer becomes the maindirection of the research of a novel display device at present.

SUMMARY

The present disclosure provides a quantum dot light-emitting deviceincludes a first electrode layer, a quantum dot light-emitting layer, anelectron transport layer, a second electrode layer and a third electrodelayer which are sequentially arranged in a stacked mode, and the side,away from the first electrode layer, of the third electrode layer isconfigured as a light exiting side; and the second electrode layer andthe third electrode layer are transparent electrode layers, and the workfunction of the second electrode layer is larger than the LUMO energylevel of the electron transport layer and smaller than the work functionof the third electrode layer.

Optionally, the oxygen content of the material of the second electrodelayer is smaller than the oxygen content of the material of the thirdelectrode layer.

Optionally, the thickness of the second electrode layer is smaller thanthat of the third electrode layer.

Optionally, the thickness of the second electrode layer is 5%-20% of thethickness of the thickness of the third electrode layer.

Optionally, the thickness of the second electrode layer is 1 nm-10 nm;and the thickness of the third electrode layer is 60 nm-100 nm.

Optionally, the second electrode layer is an indium zinc material withthe oxygen content being 0; and the third electrode layer is an indiumzinc oxide material.

Optionally, the material of the electron transport layer is zinc oxidenanoparticles or zinc oxide nanoparticles doped with magnesium.

Optionally, the quantum dot light-emitting device further includes ahole injection layer and a hole transport layer which are positionedbetween the first electrode layer and the quantum dot light-emittinglayer; and the hole injection layer is positioned between the firstelectrode layer and the hole transport layer.

Optionally, the material of the hole injection layer is an organicinjection material or an inorganic oxide.

Optionally, the material of the hole transport layer is an organictransport material or an inorganic oxide.

Optionally, the quantum dot light-emitting device further includes abase substrate; the base substrate is positioned on the side, away fromthe third electrode layer, of the first electrode layer, or the basesubstrate is positioned on the side, away from the first electrodelayer, of the third electrode layer.

The present disclosure further provides a preparation method of thequantum dot light-emitting device includes:

respectively preparing a first electrode layer, a quantum dotlight-emitting layer, an electron transport layer, a second electrodelayer and a third electrode layer, the first electrode layer, thequantum dot light-emitting layer, the electron transport layer, thesecond electrode layer and the third electrode layer are sequentiallystacked, and configuring the side, away from the first electrode layer,of the third electrode layer as a light exiting side; wherein the secondelectrode layer and the third electrode layer are transparent electrodelayers, and the work function of the second electrode layer is greaterthan the LUMO energy level of the electron transport layer and smallerthan the work function of the third electrode layer.

Optionally, preparation of the second electrode layer and the thirdelectrode layer includes:

depositing the second electrode layer and third electrode layer in asputtering mode, wherein the flow of oxygen fed during sputtering of thesecond electrode layer is smaller than the flow of oxygen fed duringsputtering of the third electrode layer.

Optionally, preparation of the second electrode layer includes:

depositing an indium zinc oxide film in a sputtering mode, wherein theflow of oxygen is about 0 sccm to 0.2 sccm and the flow of inert gas isabout 40 sccm to 60 sccm during sputtering.

Optionally, preparation of the third electrode layer includes:

depositing an indium zinc oxide film in a sputtering mode, wherein theflow of oxygen is about 0.5 sccm to 2 sccm and the flow of inert gas isabout 40 sccm to 60 sccm during sputtering.

Optionally, the preparation method further includes:

respectively preparing a hole injection layer and a hole transportlayer; wherein the hole injection layer and the hole transport layer arepositioned between the first electrode layer and the quantum dotlight-emitting layer, and the hole injection layer is positioned betweenthe first electrode layer and the hole transport layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structure diagram of a quantum dot light-emitting deviceprovided by an embodiment of present disclosure;

FIG. 2 is a structure diagram of the quantum dot light-emitting deviceprovided by another embodiment of the present disclosure;

FIG. 3 is a structure diagram of the quantum dot light-emitting deviceprovided by another embodiment of the present disclosure;

FIG. 4 is a structure diagram of an energy level structure of thequantum dot light-emitting device provided by an embodiment of thepresent disclosure;

FIG. 5 is a flow chart of a preparation method of the quantum dotlight-emitting device provided by an embodiment of the presentdisclosure;

FIG. 6 is a relational graph of the flow of oxygen and the work functionprovided by an embodiment of the present disclosure;

FIG. 7 is a change curve of transmittance of light with differentwavelengths when the light passes through different indium zinc oxidefilms according to an embodiment of the present disclosure;

FIG. 8 is a curve graph of change of light exiting intensity of a QLEDdevice along with change of thickness of a second electrode layer;

FIG. 9 is a curve graph of change of light exiting brightness of theQLED device along with change of working voltage; and

FIG. 10 is a curve graph of change of current efficiency of the QLEDdevice along with change of the light exiting brightness.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Technical solutions in embodiments of the present disclosure will bedescribed clearly and completely hereinafter in conjunction with theaccompanying drawings in embodiments of the present disclosure, andobviously, the described embodiments are only a part of, but not all,embodiments of the present disclosure. Based on the embodiments of thepresent disclosure, all other embodiments obtained by those skilled inthe art without creative work belong to the scope of protection of thepresent disclosure.

As shown in FIG. 1 to FIG. 3, the present disclosure provides a quantumdot light-emitting device, the quantum dot light-emitting deviceincludes a first electrode layer 2, a quantum dot light-emitting layer5, an electron transport layer 6, a second electrode layer 7 and a thirdelectrode layer 8 which are sequentially arranged in a stacked manner.Specifically, the side, away from the first electrode layer 2, of thethird electrode layer 8 is configured as a light exiting side, thesecond electrode layer 7 and the third electrode layer 8 are transparentelectrode layers, and the work function of the second electrode layer 7is greater than the LUMO energy level of the electron transport layer 6and smaller than the work function of the third electrode layer 8.Optionally, each transparent electrode layer is an electrode layerprepared from transparent conductive oxide materials such as an indiumtin oxide (ITO), an indium zinc oxide (IZO) and a fluorine-doped tinoxide (FTO).

According to the quantum dot light-emitting device provided by theembodiment of the present disclosure, the second electrode layer isarranged on the electron transport layer, the third electrode layer isarranged on the second electrode layer, the second electrode layer andthe third electrode layer are configured as light exiting side electrodestructures, the second electrode layer and the third electrode layer areboth transparent electrode layers, and therefore, compared with aconventional structure adopting a metal film as a light exiting sideelectrode, the quantum dot light-emitting device is higher in lightexiting efficiency; and moreover, the work function of the secondelectrode layer is smaller than the work function of the third electrodelayer, so that the work function of the second electrode layer is closerto the LUMO energy level of the electron transport layer, injection ofelectrons is facilitated, the work function of the third electrode layeris larger, the transmittance is higher, the transmittance of the lightexiting side electrode is improved favorably, and the light extractionefficiency is further improved.

Further, the second electrode layer and the third electrode layer aretransparent electrode layers and have a weak microcavity effect, and thedefects that the microcavity structure cannot be accurately controlleddue to the fact that inorganic materials such as quantum dots form afilm by adopting a solution process and the film thickness uniformity isinsufficient are overcome.

In conclusion, the quantum dot light-emitting device provided by theembodiment of the present disclosure is relatively good inlight-emitting performance and relatively high in light exitingefficiency.

As shown in FIG. 2 and FIG. 3, in a specific embodiment, the quantum dotlight-emitting device provided by the present disclosure furtherincludes a hole injection layer 3 and a hole transport layer 4 which arepositioned between the first electrode layer 2 and the quantum dotlight-emitting layer 5; wherein the hole injection layer 3 is positionedbetween the first electrode layer 2 and the hole transport layer 4. Thequantum dot light-emitting device provided by the present disclosureincludes a first electrode layer 2, a hole injection layer 3, a holetransport layer 4, a quantum dot light-emitting layer 5, an electrontransport layer 6, a second electrode layer 7 and a third electrodelayer 8 which are sequentially arranged in a stacked manner. FIG. 4 is astructure diagram of the energy level structure of the quantum dotlight-emitting device. The energy levels of the hole injection layer 3,the hole transport layer 4, the quantum dot light-emitting layer 5 andthe electron transport layer 6 are sequentially reduced, the workfunction of the second electrode layer 7 is smaller than that of thethird electrode layer 8 and is closer to the LUMO energy level of theelectron transport layer 6, and the work function of the third electrodelayer 8 is larger than that of the second electrode layer 7 and greatlydiffers from the LUMO energy level of the electron transport layer 6.

Optionally, the oxygen content of the material of the second electrodelayer 7 is smaller than that of the material of the third electrodelayer 8.

Optionally, the second electrode layer 7 is made of an indium zinc oxidematerial; and the third electrode layer 8 is made of an indium zincoxide material.

Optionally, the transmittances and the work functions of the indium zincoxide films with different oxygen contents are different, and the workfunction of the indium zinc oxide film (the second electrode layer) withlow oxygen content in the quantum dot light-emitting device is close tothe LUMO energy level of the electron transport layer, so that injectionof electrons is facilitated; and the transmittance of the indium zincoxide film (the third electrode layer) with high oxygen content ishigher than that of the indium zinc oxide film (the second electrodelayer) with low oxygen content, so that the transmittance of the indiumzinc oxide film is favorably improved, and the light extractionefficiency is further improved.

Optionally, the thickness of the second electrode layer 7 is smallerthan that of the third electrode layer 8.

Optionally, the thickness of the second electrode layer 7 is 5%-20% ofthe thickness of the third electrode layer 8.

Optionally, the thickness of the second electrode layer 7 is 1 nm-10 nm;and the thickness of the third electrode layer 8 is 60 nm-100 nm.Exemplarily, the thickness of the second electrode layer 7 may be 10 nm;and the thickness of the third electrode layer 8 may be 80 nm.

In a specific embodiment, the quantum dot light-emitting device providedby the present disclosure further includes a base substrate; optionally,as shown in FIG. 2, the base substrate 1 may be positioned on the side,facing away from the third electrode layer 8, of the first electrodelayer 2; alternatively, as shown in FIG. 3, the base substrate 1 mayalso be positioned on the side, facing away from the first electrodelayer 2, of the third electrode layer 8. That is, the quantum dotlight-emitting device provided by the present disclosure can be a bottomemitting device or a top emitting device.

In the quantum dot light-emitting device, the base substrate can beglass or a flexible PET base and the like, and the material of the basesubstrate is selected according to actual conditions and is not limitedherein.

Optionally, the deposition material of the electron transport layer ispreferably zinc oxide (ZnO) nanoparticles or zinc oxide (ZnO)nanoparticles doped with magnesium.

Optionally, the material of the first electrode layer is ITO/Ag/ITO; andof course, the material of the first electrode layer can also be atransparent indium tin oxide (ITO), a fluorine-doped tin oxide (FTO), aconductive polymer and the like or non-transparent metal electrodes suchas aluminum (Al) and silver (Ag), and the material of the firstelectrode layer is selected according to actual conditions, and is notlimited herein.

Optionally, the material of the hole injection layer can be an organicinjection material, such as PEDOT: PSS, or can be an inorganic oxide,such as a molybdenum oxide (MoO_(x)) material, is selected according toactual conditions and is not limited herein.

Optionally, the material of the hole transport layer can be an organictransport layer material, such as polyvinyl carbazole (PVK), TFB and atetraphenyl biphenyl diamine (TPD) compound, can also be an inorganicoxide, such as nickel oxide (NiO_(x)) or vanadium oxide (VO_(x)), isselected according to actual conditions and is not limited herein.

Based on the same inventive concept, the present disclosure alsoprovides a preparation method of the quantum dot light-emitting device,and the preparation method includes the following steps:

a first electrode layer, a quantum dot light-emitting layer, an electrontransport layer, a second electrode layer and a third electrode layerare prepared respectively, the first electrode layer, the quantum dotlight-emitting layer, the electron transport layer, the second electrodelayer and the third electrode layer are sequentially stacked, and theside, facing away from the first electrode layer, of the third electrodelayer is configured as a light exiting side; wherein the secondelectrode layer and the third electrode layer are transparent electrodelayers, and the work function of the second electrode layer is greaterthan the LUMO energy level of the electron transport layer and smallerthan the work function of the third electrode layer.

According to the quantum dot light-emitting device obtained through thepreparation method of the quantum dot light-emitting device, the lightexiting side electrode structure includes a double-layered structureincluding the second electrode layer and the third electrode layer, andthe second electrode layer and the third electrode layer are transparentelectrode layers, so that compared with a conventional structureadopting a metal film as a light exiting side electrode, the quantum dotlight-emitting device has the advantages that the light exitingefficiency is higher; moreover, because the work function of the secondelectrode layer is greater than the LUMO energy level of the electrontransport layer and smaller than the work function of the thirdelectrode layer, namely, the work function of the second electrode layeris smaller than the work function of the third electrode layer, the workfunction of the second electrode layer is closer to the LUMO energylevel of the electron transport layer, injection of electrons isfacilitated, the work function of the third electrode layer isrelatively large, the transmittance is relatively high, thetransmittance of a top electrode of the quantum dot light-emittingdevice is favorably improved, and the light extraction efficiency of thequantum dot light-emitting device is further improved.

Further, in the preparation method, the second electrode layer and thethird electrode layer are prepared into the transparent electrodelayers, so that the quantum dot light-emitting device has a weakmicrocavity effect, and the defect that the microcavity structure cannotbe accurately controlled due to the fact that inorganic materials suchas quantum dots form a film by adopting a solution process and the filmthickness uniformity is insufficient is overcome.

In conclusion, the quantum dot light-emitting device obtained by thepreparation method provided by the embodiment of the present disclosureis relatively good in light-emitting performance and relatively high inlight exiting efficiency.

In a specific embodiment, the preparation method of the quantum dotlight-emitting device provided by the present disclosure can furtherinclude the following step:

the hole injection layer and the hole transport layer are respectivelyprepared; and the hole injection layer and the hole transport layer arepositioned between the first electrode layer and the quantum dotlight-emitting layer, and the hole injection layer is positioned betweenthe first electrode layer and the hole transport layer.

Optionally, as shown in FIG. 5, the preparation method of the quantumdot light-emitting device provided by the present disclosure canspecifically include the following steps:

S101: the first electrode layer is formed on the base substrate;

S102: the hole injection layer is formed on the first electrode layer;

S103: the hole transport layer is formed on the hole injection layer;

S104: the quantum dot light-emitting layer is formed on the holetransport layer;

S105: the electron transport layer is formed on the quantum dotlight-emitting layer; and

S106: the second electrode layer is formed on the electron transportlayer, and the third electrode layer is formed on the second electrodelayer; wherein the second electrode layer and the third electrode layerare transparent electrode layers, and the work function of the secondelectrode layer is greater than the LUMO energy level of the electrontransport layer, and smaller than the work function of the thirdelectrode layer.

Optionally, in the preparation method of the embodiment of the presentdisclosure, preparation of the second electrode layer and the thirdelectrode layer may specifically include:

the second electrode layer and the third electrode layer are depositedin a sputtering manner, and the flow of oxygen fed during sputtering ofthe second electrode layer is smaller than that of oxygen fed duringsputtering of the third electrode layer. The flow of the fed oxygenrefers to the volume of the oxygen fed every minute.

Optionally, the second electrode layer can be a first indium zinc oxidefilm formed by sputtering deposition with low oxygen content; and thethird electrode layer can be a second indium zinc oxide film formed bysputtering deposition with high oxygen content.

Optionally, the low oxygen content is about 0 sccm to 0.2 sccm. The highoxygen content is about 0.5 sccm to 2 sccm.

Optionally, in the manufacturing process, the ratio of oxygen to inertgas in the process gas, namely the oxygen content, is controlled bycontrolling the flow of oxygen.

Optionally, during sputtering deposition of the second electrode layer,the flow of oxygen is 0 sccm-0.2 sccm, and the flow of inert gas is 40sccm-60 sccm; and during sputtering deposition of the third electrodelayer, the flow of oxygen is 0.5 sccm-2 sccm, and the flow of inert gasis 40 sccm-60 sccm.

Optionally, in the preparation method of the embodiment of the presentdisclosure, preparation of the second electrode layer includes thefollowing step:

an indium zinc oxide (IZO) film is deposited on the electron transportlayer in a sputtering manner, during sputtering, the flow of oxygen isabout 0 sccm to 0.2 sccm, and the flow of inert gas is about 40 sccm to60 sccm, wherein ‘about’ means that the error range is within 20%, forexample, in an actual operation process, the flow of oxygen may also be2.1 sccm, 2.2 sccm, 2.3 sccm and 2.4 sccm; and the meaning of thefollowing ‘about’ is the same as that of ‘about’ here.

Optionally, in the preparation method of the embodiment of the presentdisclosure, preparation of the third electrode layer includes thefollowing step:

an indium zinc oxide (IZO) film is deposited on the second electrodelayer in a sputtering manner, during sputtering, the flow of oxygen isabout 0.5 sccm to 2 sccm, and the flow of inert gas is about 40 sccm to60 sccm.

In the preparation method of the quantum dot light-emitting device, theinert gas can be argon.

In the preparation method of the quantum dot light-emitting device, thetransmittances and the work functions of the indium zinc oxide filmsdeposited by different flows of oxygen are different, wherein the workfunction of the IZO film deposited at the low flow of oxygen (O sccm to0.2 sccm) is close to the LUMO energy level of the electron transportlayer, injection of electrons is facilitated, the transmittance of theIZO film deposited at the high flow of oxygen (0.5 sccm to 2 sccm) ishigher than that of the IZO film deposited at the low flow of oxygen,the transmittance of the IZO film is improved favorably, and thus, thelight extraction efficiency is improved.

Optionally, in the preparation method provided by the embodiment of thepresent disclosure, the sputtering time of the third electrode is longerthan that of the second electrode. That is, the film thickness of thethird electrode layer formed by sputtering is greater than the filmthickness of the second electrode layer formed by sputtering.

In addition, in order to better illustrate the performance of thequantum dot light-emitting device provided by the present disclosure,the present disclosure also provides some specific experimental data.

FIG. 6 represents a relational curve of the flow of oxygen fed in theindium zinc oxide film layer preparation process and the work functionof the indium zinc oxide film layer obtained through experiments, andspecifically shows a work function change curve of the flow of oxygen ina range of 0-2.0 sccm; FIG. 7 shows a change curve of the transmittanceof light with different wavelengths when the light passes throughdifferent indium zinc oxide films, wherein process conditions of theindium zinc oxide films in the curve A are as follows: the workingpressure is 0.4 Pa, the flow of oxygen is 0 sccm, the flow of argon is40 sccm, and the process time is 1800 s; the process conditions of theindium zinc oxide films in the curve B are as follows: the workingpressure is 0.4 Pa, the flow of oxygen is 0.8 sccm, the flow of argon is40 sccm, and the process time is 1800 s; the process conditions of theindium zinc oxide films in the curve C are as follows: the workingpressure is 0.4 Pa, the flow of oxygen is 1.6 sccm, the flow of argon is40 sccm, and the process time is 1800 s; the process conditions of theindium zinc oxide films in the curve D are as follows: the workingpressure is 0.6 Pa, the flow of oxygen is 1.6 sccm, the flow of argon is40 sccm, and the process time is 1200 s; and the process conditions ofthe indium zinc oxide films in the curve E are as follows: the workingpressure is 0.8 Pa, the flow of oxygen is 1.6 sccm, the flow of argon is40 sccm, and the process time is 900 s. The process time corresponds tothe thickness of the indium zinc oxide film, and it can be seen fromFIG. 7 that the influence of the working pressure and the thickness ofthe film on the transmittance is not large, and the influence of theflow of oxygen on the transmittance is large.

Optionally, as shown in FIG. 6 and FIG. 7, when at the low flow ofoxygen, for example, the flow of oxygen is 0 sccm (for example, curveA), the work function of the deposited IZO film is low, is about 4.2 eV,and is close to the LUMO energy level of the electron transport layer,injection of the electrons is facilitated, but the transmittance is only30% to 40%, when at the high flow of oxygen, for example, the flow ofoxygen is 1.6 sccm (for example, curves C, D and E), the work functionof the deposited IZO film is about 5.6 eV, and greatly differs from theLUMO energy level of the electron transport layer, injection of theelectrons is not facilitated, but the transmittance can reach 90% orabove, therefore, the transparent top electrode is of a two-layerstructure, a mode of depositing at the low flow of oxygen is adopted forthe second electrode layer close to the electron transport layer inconsideration of two factors of the energy level and the transmittance,injection of the electrons is facilitated, a mode of depositing at thehigh flow of oxygen is adopted for the third electrode layer, thus, thetransmittance of the top electrode is favorably improved, and the lightextraction efficiency of the top electrode is further improved.

In specific experimental data, the inventor also carries out comparativeexperimental analysis on the QLED device (the top electrode includes twoIZO layers with different work functions) provided by the embodiment ofthe present disclosure and a conventional QLED device (the top electrodeis a single IZO layer). Specifically, the same experimental conditionsof the two QLED devices are as follows: the bottom electrode material isIZO/Ag/IZO, the hole injection layer (HI) and the hole transport layer(HT) are organic materials, the QD material is cadmium selenide (CdSe),and the electron transport layer (ETL) adopts zinc oxide nanoparticles.Differences between the two QLED devices are as follows.

In the conventional QLED device, the preparation conditions of thesingle IZO layer of the top electrode are as follows: the flow of argonis 40 sccm, the flow of oxygen is 2 sccm, the working pressure is 0.5Pa, and the process time is 20-30 min.

According to the QLED device provided by the embodiment of the presentdisclosure, in the two IZO layers of the top electrode, the layer closeto the ETL is IZO1, the layer away from the ETL is IZO2, wherein thepreparation conditions of IZO1 are as follows: the flow of argon is 40sccm, the flow of oxygen is 0 sccm, the working pressure is 0.5 Pa, theprocess time is 2-5 min, and the thickness is 10 nm; and the preparationconditions of IZO2 are as follows: the flow of argon is 40 sccm, theflow of oxygen is 2 sccm, the working pressure is 0.5 Pa, the processtime is 20-30 min, and the thickness is 80 nm. As shown in FIG. 8, thethickness of the IZO2 film and the light exiting intensity of the QLEDdevice are in multi-sine wave distribution through optical simulation,and the peak of the sine wave is gradually reduced, wherein the maximumcentral peak of wave is 80 nm, that is, when the thickness of the IZO2film is 80 nm, the light exiting efficiency is the highest.

Optionally, FIG. 9 is a curve graph of change of light exitingbrightness (L) of the QLED device along with change of working voltage(Voltage), and specifically shows a light exiting brightness changecurve of the voltage in a range of 4-8 V; wherein FIG. 9(a) is a curveof change of light exiting brightness (L) of the conventional QLEDdevice along with change of the working voltage (Voltage), and FIG. 9(b)is a curve of light exiting brightness (L) of the QLED device providedby the embodiment of the present disclosure along with change of workingvoltage (Voltage). FIG. 10 is a curve graph of current efficiency (C.E.)of the QLED device along with change of the light exiting brightness(L), and specifically shows a curve of change of the current efficiencyof voltage in a range of 4-8 V along with change of the brightness;wherein FIG. 10(a) is a curve of change of the current efficiency (C.E.)of the conventional QLED device along with change of the light exitingbrightness (L), and FIG. 10(b) is a curve of change of the currentefficiency (C.E.) of the QLED device provided by the embodiment of thepresent disclosure along with change of the light exiting brightness(L).

As can be seen from comparison of (a) and (b) in FIG. 9, the lightexiting brightness of the QLED device provided by the embodiment of thepresent disclosure is obviously improved and multiplied compared withthat of the conventional QLED device, and specifically, when the workingvoltage is 5-6 v, the light exiting brightness of the QLED deviceprovided by the embodiment of the present disclosure can even reach 10times that of the conventional QLED device or above. As can be seen fromcomparison of (a) and (b) in FIG. 10, the current efficiency of the QLEDdevice provided by the embodiment of the present disclosure is obviouslyimproved compared with that of the conventional QLED device, andspecifically, when the working voltage is 5-6 v, the current efficiencyof the QLED device provided by the embodiment of the present disclosureis approximately 62 cd/A-63 cd/A and is about 2 times that of theconventional QLED device (32 cd/A-38 cd/A). In conclusion, experimentaldata results show that compared with a conventional QLED device, theQLED device provided by the embodiment of the present disclosure has theadvantages that the light exiting brightness and the current efficiencyare remarkably improved, and the performance of the QLED device can beeffectively improved.

It will be apparent to those skilled in the art that various changes andmodifications can be made in the embodiments of the present disclosurewithout departing from the spirit and scope of the present disclosure.Thus, if such modifications and variations of the present disclosurefall within the scope of the claims of the present disclosure and theirequivalents, the present disclosure is also intended to include suchmodifications and variations.

1. A quantum dot light-emitting device, comprising a first electrode layer, a quantum dot light-emitting layer, an electron transport layer, a second electrode layer and a third electrode layer which are sequentially arranged in a stacked mode, wherein a side, away from the first electrode layer, of the third electrode layer is configured as a light exiting side; and the second electrode layer and the third electrode layer are transparent electrode layers, and a work function of the second electrode layer is greater than a LUMO energy level of the electron transport layer and smaller than a work function of the third electrode layer.
 2. The quantum dot light-emitting device according to claim 1, wherein an oxygen content of material of the second electrode layer is smaller than an oxygen content of material of the third electrode layer.
 3. The quantum dot light-emitting device according to claim 1, wherein a thickness of the second electrode layer is smaller than a thickness of the third electrode layer.
 4. The quantum dot light-emitting device according to claim 3, wherein the thickness of the second electrode layer is 5%-20% of the thickness of the third electrode layer.
 5. The quantum dot light-emitting device according to claim 4, wherein the thickness of the second electrode layer is 1 nm-10 nm; and the thickness of the third electrode layer is 60 mn-100 nm.
 6. The quantum dot light-emitting device according to claim 1, wherein the second electrode layer is an indium zinc material with an oxygen content being 0; and the third electrode layer is an indium zinc oxide material.
 7. The quantum dot light-emitting device according to claim 1, wherein a material of the electron transport layer is zinc oxide nanoparticles or zinc oxide nanoparticles doped with magnesium.
 8. The quantum dot light-emitting device according to claim 1, further comprises a hole injection layer and a hole transport layer which are positioned between the first electrode layer and the quantum dot light-emitting layer; and the hole injection layer is positioned between the first electrode layer and the hole transport layer.
 9. The quantum dot light-emitting device according to claim 8, wherein a material of the hole injection layer is an organic injection material or an inorganic oxide.
 10. The quantum dot light-emitting device according to claim 8, wherein a material of the hole transport layer is an organic transport material or an inorganic oxide.
 11. The quantum dot light-emitting device according to claim 1, further comprises a base substrate; and the base substrate is positioned on a side, away from the third electrode layer, of the first electrode layer, or the base substrate is positioned on a side, away from the first electrode layer, of the third electrode layer.
 12. A preparation method of the quantum dot light-emitting device, comprising: respectively preparing a first electrode layer, a quantum dot light-emitting layer, an electron transport layer, a second electrode layer and a third electrode layer, wherein the first electrode layer, the quantum dot light-emitting layer, the electron transport layer, the second electrode layer and the third electrode layer are sequentially stacked, and configuring a side, away from the first electrode layer, of the third electrode layer as a light exiting side; wherein the second electrode layer and the third electrode layer are transparent electrode layers, and a work function of the second electrode layer is greater than a LUMO energy level of the electron transport layer and smaller than a work function of the third electrode layer.
 13. The preparation method according to claim 12, wherein the preparing the second electrode layer and the third electrode layer comprises: depositing the second electrode layer and the third electrode layer in a sputtering mode, wherein a flow of oxygen fed during sputtering of the second electrode layer is smaller than a flow of oxygen fed during sputtering of the third electrode layer.
 14. The preparation method according to claim 13, wherein the preparing the second electrode layer comprises: depositing an indium zinc oxide film in a sputtering mode, wherein the flow of oxygen is about 0 sccm to 0.2 sccm and a flow of inert gas is about 40 sccm to 60 sccm during sputtering.
 15. The preparation method according to claim 13, wherein the preparing of the third electrode layer comprises: depositing an indium zinc oxide film in a sputtering mode, wherein the flow of oxygen is about 0.5 sccm to 2 sccm and a flow of inert gas is about 40 sccm to 60 sccm during sputtering.
 16. The preparation method according to claim 12, further comprising: respectively preparing a hole injection layer and a hole transport layer; wherein the hole injection layer and the hole transport layer are positioned between the first electrode layer and the quantum dot light-emitting layer, and the hole injection layer is positioned between the first electrode layer and the hole transport layer. 